1. Field of the Invention
This invention pertains generally to the field of physiological data recording and transmission devices, and more particularly to gamma ray radioisotope cameras and associated data processing equipment.
2. Description of the Prior Art
A number of radioisotope cameras have been developed for viewing the distribution of radioisotope materials in the bodies of humans and other animals. Such cameras record the entire field of view continuously in contrast to the somewhat older technique of scanning the subject point by point. Radioisotope cameras have become commonplace for diagnositic and research purposes and are extensively used in hospitals and research organizations. See e.g. Hal O. Anger, Radioisotope Cameras, Chapter 19, Instrumentation in Nuclear Medicine, Academic Press, Inc. 1967.
In particular, the gamma ray scintillation camera has become the most commonly utilized radioisotope camera because of its sensitivity and adaptability. The scintillation camera employs a solid sodium iodide scintillation crystal which gives off a point flash of visible light when a gamma ray impinges upon it. An array of photomultiplier tubes are spaced behind the sodium iodide crystal and perform the function of translating the point flashes of light to a pulse of electric current at the outputs of the photomultiplier tubes. The magnitude of the pulse of output current at each tube in the array is proportional to the amount of light which strikes the tube. The position of a single flash of light in the sodium iodide crystal can be determined by comparing the magnitude of the outputs of each photomultiplier tube in the array, since each photomultiplier tube will receive an amount of light from the flash which depends upon the angle and distance of the point flash from the tube. The outputs of the photomultiplier tube can be combined by means of electronic circuitry to yield output signals which are proportional to the position coordinates of the point flash of light, and the intensity of the flash of light. The "picture" seen by the camera may be viewed by utilizing these signals to provide the "X" and "Y" inputs to an oscilloscope, with the electrical signal corresponding to intensity being used to control the electron beam intensity of the oscilloscope. The gamma ray image may be focused upon the sodium iodide crystal by means of a pinhole collimator, or more commonly, by means of a multi-channel collimator having numerous channels formed in a gamma ray absorber plate.
The output signals from the gamma ray scintillation camera may also be utilized to provide quantitative information in addition to the pictorial display of the density of gamma ray emissions in a subject. This may be accomplished by feeding the outputs of the gamma ray camera to a digital computer for processing. The signals corresponding to the X and Y location of the flash of light, and the signal corresponding to the magnitude of the flash, are digitized before being supplied to the computer. For purposes of the computing scheme, the recording face of the gamma ray camera is commonly divided up into a rectangular grid containing a large number of small rectangular cells. The computer determines, from the input signal supplied to it from the gamma camera, at which cell on the face of the gamma camera the point flash occurred. The computer is capable of counting the number of flashes that occur in each cell over a specified period of time, such as one second, and will maintain this number in the memory of the computer. The computer will then begin counting over again for each cell for another predetermined unit of time to determine the number of point flashes occurring at that cell over that unit of time. It is thus possible to have the computer read out the number of gamma point flashes that occurred in any particular cell as a function of time. It is also possible to read out the number of point flashes that occurred in any desired group of cells as a function of time. This procedure is of special value in the examination of dynamically active body organs such as the heart and the kidneys. It is possible, for example, to delineate the area of a gamma ray camera image which corresponds to a ventricle of the heart. The flow of blood containing a radioactive isotope through the ventricle can then be measured by using the computer to determine the change in the number of gamma ray emissions seen by the camera in the area of the ventricle as a function of the time. The internal programming of the computer can be utilized to allow selection of the cells that correspond to the ventricular area of the heart.
It is often desirable to correlate the dynamic information obtained from the gamma ray camera pictures of an organ with other physiological data information concerning that organ, or concerning related body functions, which are obtained from other physiological sensors. For example, it is desirable to be able to correlate blood pressure and electro-cardiogram (ECG) readings in time synchrony with the gamma ray scintillation camera data concerning the flow through a heart ventricle. It is extremely difficult to acquire the data from the various sensors first, and then attempt to correlate them in time synchrony at a later time. It would be highly desirable to be able to provide the physiological data from the sensors to the computer at the same time that the data is being provided thereto by the gamma ray camera. However, this would require an extensive modification of existing computers, or the use of a larger and more expensive computer with more extensive programming. Such modifications are difficult to implement and have been prohibitively expensive for the common medical applications of the gamma ray camera.